The purpose of the proposed research is to investigate the mechanisms of binocular vision responsible for stereoscopic depth perception in two animals representing various stages of primate evolution, the tree shrew (Tupaia glis) and the bushbaby (Galgo senegalensis), and in a predatory nonmammalian, the falcon (Falco sparverius), known to possess the capacity for stereopsis. In the tree shrew, behavioral tests of visual resolution and of stereopsis will be carried out in animals before and after cortical ablation. In the bushbaby, behavioral tests of stereoposis will be performed. In the falcon, neuroanatomical investigations of the pathways subserving binocular vision will be performed. The research builds on prior work, which has developed methods for testing stereopsis in the cat and in the falcon. Of major concern are the neural structures essential for stereopsis in animals representing different lines of descent. It is anticipated that the work will contribute to an understanding of the development of binocular vision in higher primates, including humans, and will bear upon the resolution of anomalies of binocular vision, such as those attendant to strabismic amblyopia.